John & Jessica: One Carpet, Two Entrances?

Just who was that with John Mayer on the red carpet at the New York Met Costume Gala last night? All we know is that it wasn't Jessica Simpson - after all, given how, er, on display Jess was last night, we would have been hard-pressed to miss her by John's side! Could there be trouble in paradise already for John & Jessica? Let's hope not - they were only just starting to get boring together!